1. Field of the Invention
This invention relates to steels for hot working press tools used in the continuous reduction of slab width.
2. Related Art Statement
When slabs of various sizes are produced by the continuous casting method, it is necessary to provide a mold for continuous casting in correspondence to each size of the slabs, so that there is a problem of decreasing the productivity through the exchange of the mold. Therefore, it is desired to arrange various sizes of the molds into some typical sizes.
For this purpose, there has been developed a slab width sizing press (hereinafter referred to as sizing press) in which the width of the hot slab after the continuous casting is reduced in the widthwise direction over a full length of the slab ranging from the head to the tail in accordance with a size of the slab to be reduced, by repeatedly applying a pressure in the widthwise direction to the hot slab through a pressing tool (hereinafter referred to as anvil) every relative feeding of the slab to the anvil. In this case, the anvil used in the sizing press is subjected to a thermal load, so that the cracking due to thermal stress may result. Therefore, an anvil having a high resistance to thermal fatigue is demanded for preventing a decrease of productivity through the exchange of the anvil.
The steels for hot working used in a press die, forging die and the like have a standard according to JIS G4404 together with steels for cutting tools, impact tools, cold working dies and the like, some of which are disclosed in Japanese Patent Application Publication No. 54-38,570.
These steels for hot working are sufficiently durable for ordinary hot working, but are still insufficient for use in the anvil in the sizing press. The anvil for the sizing press is large in size and is continuously used for the hot slab above 1,200.degree. C., so that the temperature of the anvil becomes high up to the deep inside thereof as compared with the hot rolling roll. Consequently excessive thermal stress is caused during cooling and there is a problem of causing cracking due to thermal fatigue.